1. Field of the Invention
The present invention relates to a thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source, and more particularly, to a TFT-LCD having a photo sensor.
2. Description of the Prior Art
Display devices that have a back light source such as a liquid crystal display (LCD) are usually used in portable electronic devices such as a notebook, an electronic dictionary, and a personal digital assistant (PDA) etc. When users utilize the display device that has the back light source, ambient illumination affects the ability of the users to view the display device directly. Therefore, the above-mentioned portable electronic devices need a suitable light source adjusting mechanism to adjust the back light source.
The prior art light source adjusting mechanism is mainly a manual light source adjusting mechanism. The users can adjust the back light source of the display devices by way of a specific light source adjusting knob or keys of a keyboard disposed on the device. However, the prior art mechanism has two disadvantages. First, when the LCD is used in portable electronic products, the portable electronic products are usually in various background environments, such as in a moving car. Therefore the users must adjust the back light source often, causing inconvenience for the user. Second, the users could adjust the back light source to a brighter brightness level to prevent the operational inconvenience, but this leads to high power consumption.
Please refer to FIG. 1. FIG. 1 is a circuit diagram of a prior art back light adjusting circuit 10. The back light adjusting circuit 10 includes a back light source 12 for generating backlight, a photo sensor 14, an amplified circuit 16, a decisive circuit 18, and a DC/AC inverter 20. The back light source 12 and the inverter 20 are composed of a back light module, and the back light module generates the backlight with various brightness levels depending on ambient illumination 22.
When the photo sensor 14, such as a photosensitive resistance or a charge coupled device (CCD) senses the ambient illumination 22, the photo sensor 14 generates a corresponding photocurrent ip that depends on the ambient illumination 22. Since photocurrent ip generated from the photo sensor 14 is very weak, the amplified circuit 16 is used to amplify the photocurrent ip to conveniently perform the subsequent signal processes. The amplified circuit 16 includes a transistor Q1, a resistance R1 and a resistance R2, functioning as an amplifier, and a voltage source VDC for providing a bias voltage. When a base of the transistor Q1 receives a voltage signal converted from the photocurrent ip by the resistance R1, an amplified signal 24 is sent from a collector of the transistor Q1 to the decisive circuit 18 to calculate the ambient illumination 22.
The decisive circuit 18 includes a photo diode D1. An anode of the photo diode D1 receives the amplified signal 24, and then a back light control signal 26 is calculated and sent from a cathode of the photo diode D1 to the inverter 20. The inverter 20 receives the back light control signal 26 and transforms it into a current, which is used to drive the back light source 12. The inverter 20 includes a transistor Q2 for receiving a driving voltage and producing a switching voltage, a transformer T1 for transforming the switching voltage to a loading voltage for providing to the back light source 12, a pulse width modulation (PWM) controller 28 that generates a pulse width modulate signal 29 corresponding to a pulse width according to the received back light control signal 26 and transfers the pulse width modulate signal 29 to the base of the transistor Q2. By turning on and off the transistor Q2, a voltage source VM is indirectly connected to the transformer T1. And a corresponding driving current is produced so that the back light source 12 generates a corresponding back light.
When the prior art back light adjusting circuit 10 is applied to a display device (not shown), an output circuit of the inverter 20 can be modulated according to the back light control signal 26 sent from the decisive circuit 18 to adjust the back light source 12 spontaneously when the back light source 12 of the display device is turned on. However, the prior art back light adjusting circuit 10 has several disadvantages. First, the prior art back light adjusting circuit utilizes the additional photo sensor, increasing costs and volume of the display device. Second, the back light adjusting circuit is applied to the display device which has the back light source. However, for display devices which have a front light source, the ambient illumination and the front light source are on same side. Therefore, if variations of the ambient illumination are acute enough, the ability of users to view the display device will be severely affected.
It is therefore a primary objective of the claimed invention to provide a thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source that depends an ambient illumination spontaneously, without consuming power and causing eyestrain.
It is another objective of the claimed invention to provide a light source adjusting mechanism that applies to a back light source and a front light source.
According to the claimed invention, a thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source includes a liquid crystal sealed between a first substrate and a second substrate, with the second substrate having an active region and a peripheral region. The TFT-LCD also includes a pixel matrix array disposed in the active region of the second substrate, and at least one thin film transistor (TFT) functioning as a photo sensor disposed in the peripheral region of the second substrate, with the TFT having an amorphous silicon layer. The TFT-LCD further includes a feedback circuit, and a light source module that includes the light source and a light source modulator. When ambient light enters the first substrate and passes through the amorphous silicon layer of the TFT, the TFT generates a current in the feedback circuit. Then a feedback signal is sent from the feedback circuit to the light source modulator to adjust the light source of the TFT-LCD to an optimal brightness level that depends on ambient illumination.
It is an advantage that the claimed invention uses the TFT disposed in the peripheral region of the second substrate as the photo sensor to detect the ambient illumination and that the light source modulator can enhance, weaken, open, or close the light source of the TFT. Therefore, manufacturing costs are reduced, without consuming power and causing eyestrains.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.